The velocity of blood flow in a patient's legs is known to decrease during confinement in bed. Such pooling or stasis of blood is particularly pronounced during surgery, immediately after surgery, and when the patient has been confined to bed for an extended period of time. Additionally, blood stasis is a significant cause leading to the formation of thrombi in the patient's legs, which may eventually cause serious injury or even death. Additionally, in certain patients, it is desirable to move fluid out of interstitial spaces in extremity tissues in order to reduce swelling associated with edema in the extremities. By enhancing the circulation in the limb, the arterial and venous blood flow could be improved.
Intermittent pneumatic compression (IPC) devices are used to improve circulation and minimize the formation of thrombi in the limbs of patients. These devices typically include a compression sleeve or garment which wraps around the patient's limb. The sleeve has one or more separate inflatable chambers which are connected to a source of compressed fluid, generally air. The chamber or chambers are inflated to provide a compressive pulse to the limb, thereby increasing blood circulation and minimizing the formation of thrombi. In a multi-chambered sleeve, the compression pulses typically begin around the portion of the limb farthest from the heart, for example, the ankle, and progress sequentially toward the heart. The chamber or chambers are maintained in the inflated state for a predetermined duration, and all the chambers are depressurized simultaneously. After another predetermined period of time, the compression pulse repeats. Typical compression devices are described in U.S. Pat. No. 4,396,010 and U.S Pat. No. 5,876,359, filed Nov. 14, 1994, the disclosures of which are incorporated herein by reference.
Deep vein thrombosis and other venous and arterial conditions may also be diagnosed and evaluated by various air plethysmography techniques. These techniques use one or more pressure cuffs wrapped around one or more portions of a patient's limb. Volume changes of blood flow in the limb are monitored by monitoring the pressure in the cuff or cuffs with the limb in various positions and due to various position changes of the limb, often after application of a venous tourniquet to cause the limb to fill with blood. The venous tourniquet may be applied by a pressure cuff around a portion of the limb, for example, the thigh.